U.S. patent number 8,160,022 [Application Number 12/109,442] was granted by the patent office on 2012-04-17 for wireless communication system, wireless base station, wireless terminal and communication control method of the wireless communication system.
This patent grant is currently assigned to Hitachi, Ltd.. Invention is credited to Rintaro Katayama, Shiro Mazawa, Toshiyuki Saito, Keisuke Takeuchi.
United States Patent |
8,160,022 |
Mazawa , et al. |
April 17, 2012 |
Wireless communication system, wireless base station, wireless
terminal and communication control method of the wireless
communication system
Abstract
A wireless access terminal, after handoff, adds channel quality
information calculated in the wireless access terminal to a header
of transmit data and transmits this data until a wireless base
station succeeds in receiving at least one or more packets. The
wireless base station, when having succeeded in receiving a packet
for the first time after the handoff, extracts the channel quality
information from a received header to initialize channel quality
information inside the wireless base station. Subsequently, the
wireless base station autonomously updates the channel quality
information in response to success or failure of packet reception
and controls the transmission rate.
Inventors: |
Mazawa; Shiro (Fujisawa,
JP), Saito; Toshiyuki (Kyotanabe, JP),
Takeuchi; Keisuke (Kunitachi, JP), Katayama;
Rintaro (Kokubunji, JP) |
Assignee: |
Hitachi, Ltd. (Tokyo,
JP)
|
Family
ID: |
40161215 |
Appl.
No.: |
12/109,442 |
Filed: |
April 25, 2008 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20090005060 A1 |
Jan 1, 2009 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 27, 2007 [JP] |
|
|
JP-2007-117951 |
Apr 21, 2008 [JP] |
|
|
JP-2008-109737 |
|
Current U.S.
Class: |
370/331;
455/436 |
Current CPC
Class: |
H04W
28/22 (20130101); H04W 36/30 (20130101) |
Current International
Class: |
H04W
4/00 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Ly; Anh-Vu
Attorney, Agent or Firm: Antonelli, Terry, Stout &
Kraus, LLP.
Claims
The invention claimed is:
1. A wireless communication system, comprising: a plurality of
wireless base stations and a plurality of wireless access
terminals, wherein each wireless base station of the plurality of
wireless base stations including: a receiver for receiving wireless
channel quality information which is sent from a plurality of
wireless access terminals, respectively, a storage for storing the
wireless channel quality information, and a calculator to calculate
a transmission rate allocated to each of the plurality of wireless
access terminals in accordance with the wireless channel quality
information and channel quality information calculated in the
wireless base station, and wherein the calculator allocates the
calculated transmission rate; wherein each wireless access terminal
of the plurality of wireless access terminals including: a unit for
measuring a wireless channel quality; a unit for reporting the
measured wireless channel quality to a wireless base station; a
unit for receiving transmission rate allocation information from
the wireless base station; and a unit for transmitting a packet
using the allocated transmission rate; and wherein one of the
plurality of wireless base stations receives a subject packet from
a hand-off wireless access terminal which has handed off to one of
the plurality of wireless base stations, the base stations searches
a header of this subject packet to extract channel quality
information sent from the hand-off wireless access terminal, the
channel quality information being included in this subject header,
sets an initial value of the allocated transmission rate for the
hand-off wireless access terminal based on the extracted channel
quality information, and thereafter performs calculation of an
updated transmission rate for the hand-off wireless access
terminal.
2. A wireless base station, comprising: a receiver for receiving
wireless channel quality information that is sent from a plurality
of wireless access terminals, respectively; a storage for storing
the wireless channel quality information for each wireless access
terminal; a calculation unit for calculating a transmission rate
allocated to each of the plurality of wireless access terminals in
accordance with the wireless channel quality information and
channel quality information calculated in the wireless base
station; an allocation unit for allocating the calculated
transmission rate; a search unit for searching a header of a
packet; an extraction means for extracting channel quality; and
setting means for setting an initial value of the transmission
rate; and wherein upon receipt of a subject packet from a wireless
access terminal which has been handed off to the wireless base
station, to be included in the plurality of wireless access
terminals of the wireless base station: the search unit searches a
subject header of this subject packet, the extraction means
extracts channel quality information from the wireless access
terminal, the channel quality information being included in this
subject header, the setting means sets an initial value of the
transmission rate for the wireless access terminal, based on the
extracted channel quality information, and thereafter, the
calculation unit performs calculation of an updated transmission
rate allocated to the wireless access terminal.
3. The wireless communication system according to claim 1, wherein:
said each wireless access terminal further comprising: a packet
error rate calculation unit which calculates a packet error rate
based on information indicative of "ready or not ready for
reception" from the wireless base station with respect to a packet
transmitted to the wireless base station; and a unit which, after
performing a handoff to switch a base station to connect to,
inserts a packet error rate calculated in the wireless access
terminal into a packet transmitted to the wireless base station
until the unit receives information indicative of a success of
packet reception from the wireless base station to switch to.
Description
INCORPORATION BY REFERENCE
The present application claims priority from Japanese applications
JP-2007-117951 filed on Apr. 27, 2007 and JP-2008-109737 filed on
Apr. 21, 2008 the contents of which are hereby incorporated by
reference into this application.
BACKGROUND OF THE INVENTION
The present invention relates to communication control techniques
in a wireless communication system. In particular, the present
invention relates to a mobile wireless communication system using a
distributed network, in which information concerning an access
terminal is taken over between base station controllers, and to a
communication control technique for movement between a plurality of
mobile wireless communication systems.
In recent years, the use of the Internet has increased and the
environment in which the Internet can be used has also been
expanding. Especially, the ability to access the Internet using a
mobile wireless communication equipment, such as a mobile phone,
allows you to use the Internet wherever you are in the country.
As the use of the Internet increases and the environment in which
the Internet can be used expands, services provided on the Internet
have also been expanding. This results in technology needs and
technical problems concerning the Internet access. For example,
with regard to the services, for example, a higher speed in
communication channels to adapt to the delivery of large-capacity
applications, such as music/video, is required, and short delay/low
jitter and the like are required as the problem to adapt to voice
interactive communications. Also in the mobile wireless
communication system, in order to satisfy these various needs,
studies for high speed and wide band have been rapidly going
on.
In the mobile wireless communication, since there is a limit in the
available frequency resources, how to achieve high frequency-usage
efficiency and high transmission speed within a limited frequency
bandwidth is an essential key in achieving the system. Moreover,
since a wireless access terminal moves and the radio environment
always changes, it is necessary to control in response to an
environmental change. If a control in response to an environmental
change is not performed, a stable channel quality cannot be
secured. As an index of the channel quality, a packet error rate
obtained by averaging the percentage of success or failure in
receiving packets that are transmitted and received within a
wireless communication system is mainly used.
In order to satisfy the above-described conditions required for the
wireless communication system, in a wireless communication system
optimized to packets, a method of rapidly switching the
transmission rate in response to the radio environment is employed.
As such a method of rapidly switching the transmission rate in
response to the radio environment, for example, in the case of an
IxEV-DO scheme shown in 3gpp2, C. S0024B ver. 1.0, Cdma2000 High
Rate Packet Data Air Interface Specification, a wireless access
terminal itself determines the transmission rate based on the radio
environment and the channel quality condition, and periodically
reports this to a wireless base station, and communicates with this
transmission rate, thereby achieving a high-speed switching.
SUMMARY OF THE INVENTION
In a mobile wireless communication system employing an antenna
technique, such as MIMO and transmission diversity, in
communicating between a wireless access terminal and a wireless
base station, the antenna technique used between the wireless
access terminal and the wireless base station needs to be selected
suitably. For this reason, as a method of implementing the scheme
of rapidly switching the transmission rate in response to the radio
environment, a scheme such as the one in the case of the IxEV-DO
scheme, in which a wireless access terminal itself determines the
transmission rate based on the radio environment and channel
quality condition and periodically reports this result to a
wireless base station, as described in the background of the
invention, cannot achieve this object. Accordingly, a different
scheme is currently used. In the mobile wireless communication
system employing an antenna technique, such as MIMO and
transmission diversity, the transmission rate is not determined by
a wireless access terminal, but the condition of the radio
environment is periodically reported from the wireless access
terminal to the wireless base station. Then, such scheme is used
that in the wireless base station, on the basis of the condition of
the radio environment received from the wireless access terminal
and the channel quality condition calculated in the wireless base
station, the transmission rates for both the uplink and the
downlink are suitably determined along with an antenna technique
used in the wireless base station. In the wireless base station,
information, including the condition of the radio environment sent
from the wireless access terminal, is associated with the wireless
access terminal and is managed in the wireless base station.
Thus, in the case of a scheme in which a wireless base station
determines the transmission rate, in order for the wireless base
station to determine an appropriate transmission rate for both the
uplink and downlink, the wireless base station side should always
know the channel quality condition correctly.
Incidentally, in the mobile wireless communication system, along
with the movement of a wireless access terminal, a wireless base
station currently communicating with the wireless access terminal
needs to be switched during communication. This is called handoff.
As described above, in the case of the system employing an antenna
technique, a wireless base station needs to know the channel
quality condition of a wireless access terminal correctly at all
times. However, if the handoff occurred and a destination base
station of a wireless access terminal has switched over, then, in
the above-described system which will not take over the current
channel quality condition between base stations, the current
channel quality condition being known by the wireless base station
side that has been connected to, the destination wireless base
station cannot determine the channel quality accurately unless it
transmits and receives a certain amount of packets or more from the
wireless access terminal which has been handed off thereto. For
this reason, the reception quality of the wireless access terminal
will not be stabilized for a while after the handoff. If a too high
transmission rate has been allocated until the receiving condition
becomes stable, a packet error will occur frequently. On the other
hand, if a too low transmission rate has been allocated, the
throughput will decrease unduly.
On the other hand, in the case of a mobile wireless communication
system using a distributed network, in which information concerning
a wireless access terminal is taken over between base station
controllers, the current channel quality condition may be taken
over between base stations at the time of handoff. However, in this
case, such problem will occur that the service will stop for an
amount of time required to take over between base stations.
Moreover, while the establishment of such mechanism that takes over
the current channel quality information between base stations may
have an advantage in strengthening their cooperation between base
stations, it also has a problem that the system control becomes
complicated.
Moreover, the same problem will occur also when a wireless access
terminal connectable to a plurality of mobile wireless
communication systems hands off between a plurality of mobile
wireless communication systems.
The present invention has been made to solve the above-described
problems. It is an object of the present invention to provide a
communication control technique in a wireless communication system
that can provide a wireless access terminal with a stable channel
quality and high throughput even when handoff is repeated within
the same mobile communication system or between a plurality of
mobile communication systems.
In order to solve the above-described problems, in the present
invention, in transmitting the first packet after handoff, a
wireless access terminal transmits the packet including the
previous channel quality information to a wireless base station,
and the wireless base station sets this channel quality information
as the initial value of the channel quality information, and will
keep updating the subsequent channel quality information, and
control so as to determine the transmission rate based on this
information.
According to the present invention, a stable channel quality and a
high throughput can be provided to a wireless access terminal even
when handoff is repeated within a mobile communication system or
between a plurality of mobile communication systems.
Other objects and features and advantages of the invention will
become apparent from the following description of the embodiments
of the invention taken in conjunction with accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram illustrating an overall configuration of a
communication network including a wireless communication system and
the Internet, to which the present invention is applied.
FIG. 2 is a diagram illustrating a configuration of a wireless
access terminal in an embodiment of the present invention.
FIG. 3 is a diagram illustrating a configuration of a wireless base
station in the embodiment of the present invention.
FIGS. 4A and 4B are views explaining conventional packet error rate
calculation algorithms.
FIGS. 5A and 5B are views explaining packet error rate calculation
algorithms in the embodiment of the present invention.
FIG. 6 is a view illustrating a packet format in the embodiment of
the present invention.
FIG. 7 is a diagram illustrating a configuration of a wireless
access terminal in an embodiment of the present invention.
FIG. 8 is a diagram illustrating a configuration of a wireless base
station in the embodiment of the present invention.
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described
with reference to examples.
In the following embodiments, description is made on the basis of
C.S0084-0 which is under study as a next generation system for
achieving higher speed and wider bandwidth.
C.S0084-0 is a system which is under discussion for standardization
as a system two steps ahead of the current IxEV-D0. In C.S0084-0,
both uplink/downlink are based on orthogonal frequency division
multiplex access (hereinafter, referred to as OFDMA) allowing for
communication at 70 Mbps for the uplink and 280 Mbps for the
downlink.
Here, first, a rate control method in the downlink, a rate control
method in the uplink, and handoff information in C.S0084-0, which
are required to describe the embodiments of the present invention,
are described.
First, the rate control method in the downlink is described.
In a downlink, a wireless access terminal periodically measures the
reception quality of the downlink, and notifies the measurement
result to a wireless base station by using an R-CQICH (Reverse
Channel Quality Indicator Channel). The wireless base station
determines the transmission rate and frequency bandwidth to
allocate, based on the reception quality information notified from
the wireless access terminal, packet error rate information
calculated thereinside, and the amount of data buffered in the
wireless base station, and notifies this result to the wireless
access terminal by transmitting information called an FLAB (Forward
Link Assignment Block) with the use of an F-SCCH (Forward Shared
Control Channel). Moreover, the R-CQICH also has a function to
allow a wireless access terminal to designate a wireless base
station, which the wireless access terminal desires to communicate
with in the downlink. When a change occurs in a wireless base
station designated in the R-CQICH, handoff of the downlink is
carried out.
Next, the rate control method in an uplink is described.
In an uplink, a wireless access terminal notifies a wireless base
station with the amount of data, which the wireless access terminal
desires to transmit in the uplink, with the use of an R-REQCH
(Reverse Request Channel). The wireless base station determines the
transmission rate and frequency bandwidth to allocate, based on the
measured reception quality information, packet error rate
information calculated thereinside, and the notified amount of
data, and notifies the wireless access terminal by transmitting
information called an RLAB (Reverse Link Assignment Block) with the
use of the F-SCCH. Moreover, the R-REQCH also has a function to
allow a wireless access terminal to designate a wireless base
station, which the wireless access terminal desires to communicate
with in an uplink. When a change occurs in a wireless base station
designated in the R-REQCH, handoff of an uplink is carried out. The
handoff of an uplink and downlink can be carried out completely
independently.
In C.S0084-0, as described above, a means for achieving a
high-speed rate control and handoff in an uplink and downlink by
means of the dedicated channels is provided. However, a means for
taking over packet error rate information at the time of handoff is
not provided. For this reason, when handoff is repeated at high
speed, it takes time to obtain a correct packet error rate, and the
channel quality will not be stabilized for a while after the
handoff. Accordingly, such problem will occur that packet errors
occur frequently or the throughput drops unduly.
Then, in the following embodiments, such wireless-communication
control technique that can, on the basis of the technique under
study in C.S0084-0, flexibly correspond to a comprehensive range of
services provided in future and fully utilize the broad-banded
resources will be described specifically using examples.
Embodiment 1
First, an overall configuration of a network including a wireless
communication system to which the present invention is applied is
described.
FIG. 1 is a diagram illustrating an overall configuration of the
communication network including a wireless communication system, to
which the present invention is applied, and the Internet, and a
wired communication system.
As shown in FIG. 1, in the network to which the present invention
is applied, the wireless communication system is connected to the
Internet. In such a network, for example, a wireless access
terminal (AT) 101 of the wireless communication system communicates
via a wireless base station transceiver subsystem (BTS) 121 in a
receiving area 111, and accesses a server 161 in an internet
service provider (ISP) 151 on the Internet 141 via a base station
controller (BSC) 131.
FIG. 2 is a diagram illustrating a configuration of a wireless
access terminal in the embodiment of the present invention.
As shown in FIG. 2, the wireless access terminal comprises: an
antenna 201 which transmits and receives a radio wave between a
wireless base station to convert this into a high frequency signal;
an RF unit 202 which modulates and demodulates the high frequency
signal to convert into a baseband signal having a low frequency; a
data Ch modulation unit 203 which modulates transmit data to
convert into a baseband signal; a control Ch modulation unit 204
which modulates control information to convert into a baseband
signal; a control Ch demodulation unit 205 which demodulates a
received signal to extract control information; a data Ch receiving
unit 206 which demodulates and decodes a received signal to extract
received data; a data buffer 207 which temporarily buffers transmit
data; and an application processing unit 208 which processes the
application. The wireless access terminal further comprises a
packet error rate measuring unit (PER measuring unit) 209, which
updates the packet error rate based on information indicative of
"ready or not ready for reception" that comes from a wireless base
station in response to a packet transmitted to the wireless base
station. The wireless access terminal, when having performed
handoff, includes packet error rate information calculated by the
PER of the wireless access terminal into a header of a transmission
packet destined to a wireless base station and transmits this
packet to the wireless base station to be handed off. After the
handoff, the wireless access terminal includes the packet error
rate information into a header of a transmission packet and
transmits this packet until it receives information indicative of
"ready for packet reception" from the wireless base station to be
handed off.
At this point, an amount of data stored in the data buffer 207 is
notified to the control Ch modulation unit 204 by the application
processing unit, which is then notified to the wireless base
station using the R-REQCH. Moreover, the control Ch demodulation
unit 205 measures the strengths of signals, which a plurality of
wireless base stations are transmitting, and then, based on this
result, selects a wireless base station to communicate with and
measures the reception quality condition in the selected wireless
base station. These results are notified to the control Ch
modulation unit 204, which are then notified to the wireless base
station using R-CQICH. The notification to the wireless base
station is continued until the wireless base station succeeds in
receiving at least one packet.
FIG. 3 is a diagram illustrating a configuration of a base station
in the embodiment of the present invention.
As shown in FIG. 3, the wireless base station comprises: an antenna
301 which transmits and receives a radio wave between a wireless
access terminal in an area to convert this into a high frequency
signal; an RF unit 302 which modulates and demodulates the high
frequency signal to convert into a baseband signal having a low
frequency; a data Ch modulation unit 303 which modulates transmit
data to convert into a baseband signal; a control Ch modulation
unit 304 which modulates control information to convert into a
baseband signal; a control Ch demodulation unit 305 which
demodulates received signal to extract control information; a data
Ch receiving unit 306 which demodulates and decodes a received
signal to extract received data; a data buffer 307 which
temporarily buffers transmit data; a channel processing unit 308
for transmitting data to a base station controller; a scheduler 309
which determines a transmission rate from information of a received
control Ch and the like; and a PER measuring unit 310 which
calculates a packet error rate from a data demodulation result in
the data Ch demodulation unit. Here, as many control Ch
demodulation units 305 and data buffers 307 as the number
corresponding to all the wireless access terminals in an area are
prepared in advance, and as many data Ch modulation units 304 and
data Ch demodulation units 306 as the number corresponding to the
number of wireless access terminals which the scheduler 309 has
allocated are prepared in advance. The scheduler 309 determine a
transmission rate and bandwidth allocated to a wireless access
terminal on the basis of a downlink buffer amount notified from the
data buffer 307, an uplink buffer amount obtained as a result of
reception at the Ch demodulation unit, downlink/uplink signal
quality, and packet error rate information notified from the PER
measuring unit 310.
FIGS. 4A and 4B show conventional packet error rate calculation
algorithms in the PER measuring unit. Upon receipt of a packet, a
wireless base station determines which wireless access terminal the
packet corresponds to (401, 402). Then, the wireless base station
updates the average of packet error rates of the corresponding
access terminal by using an IIR filter with a time constant "a"
(403). Moreover, if the wireless access terminal has been handed
off thereto from other wireless base station, the wireless base
station initializes the packet error rate to 0 (411, 412, 413).
FIGS. 5A and 5B show packet error rate calculation algorithms in
the present embodiment.
Upon receipt of a packet, a wireless base station determines which
wireless access terminal the packet corresponds to (501, 502).
Then, the wireless base station determines, with respect to this
access terminal, whether or not the wireless base station has
succeeded in receiving a packet even once after the handoff (503).
If having succeeded in receiving a packet in the past, the wireless
base station updates the packet error rate based on information
indicative of "ready or not ready for packet reception" that is
received using the same algorithm as that of the conventional
example (504).
If having succeeded in receiving a packet for the first time from a
new wireless access terminal which has been handed off thereto,
since the packet error rate information calculated in the PER of
the wireless access terminal is included in the header of a
received packet, the wireless base station extracts this
information. Then, conventionally, with respect to a wireless
access terminal which has been handed off thereto, the wireless
base station sets the packet error rate information to 0 and then
optimizes this while transmitting and receiving packets. However,
in this embodiment, instead of setting the packet error rate
information to 0, the wireless base station uses, as the initial
value, the value of packet error rate information sent from the
wireless access terminal, the packet error rate information being
included in the header of the packet of the wireless access
terminal which has been handed off thereto. Then, the wireless base
station turns off a packet reception success flag (505). Moreover,
if the wireless access terminal has been handed off thereto from
other wireless base station, the wireless base station turns off
the packet reception success flag for initialization (511, 512,
513).
FIG. 6 shows packet formats of this embodiment.
The leading 1 bit indicates whether or not the packet error rate
information is stored. If the leading 1 bit is 0, the packet error
rate information is not stored and data is stored except in the
leading 1 bit. If the leading 1 bit is 1, the packet error rate
information is stored and the data is stored following the packet
error rate information. After handoff, the wireless access terminal
sets 1 to the leading 1 bit and transmits this packet including the
packet error rate information until it receives information
indicative of "ready for packet reception" from a wireless base
station to be handed off.
Embodiment 2
As other example, as Embodiment 2, a method of using a sum of power
control bits as the channel quality information in a system, in
which a wireless base station controls the transmission power of a
wireless access terminal, is described.
FIG. 7 is a diagram illustrating a configuration of a wireless
access terminal in an embodiment of the present invention.
As shown in FIG. 7, the wireless access terminal comprises: the
antenna 201 which transmits and receives a radio wave between a
wireless base station to convert this into a high frequency signal;
the RF unit 202 which modulates and demodulates the high frequency
signal to convert into a baseband signal having a low frequency;
the data Ch modulation unit 203 which modulates transmit data to
convert into a baseband signal; the control Ch modulation unit 204
which modulates control information to convert into a baseband
signal; the control Ch demodulation unit 205 which demodulates a
received signal to extract control information; the data Ch
receiving unit 206 which demodulates and decodes a received signal
to extract received data; the data buffer 207 which temporarily
buffers transmit data; and the application processing unit 208
which processes the application. The wireless access terminal
further comprises a power-control adder 701, which retains a sum of
all the power-control information correction values from a wireless
base station, and controls the transmission power based on this.
The wireless access terminal, when having handed off, includes a
sum of power-control information correction values into a header of
a transmission packet destined to a wireless base station and
transmits this packet to the wireless base station to be handed
off. After the handoff, the wireless access terminal includes this
information into a header of a transmission packet and transmits
this packet until it receives information indicative of "ready for
packet reception" from the wireless base station to be handed
off.
FIG. 8 is a diagram illustrating a configuration of a base station
in the embodiment of the present invention.
As shown in FIG. 8, the wireless base station comprises: the
antenna 301 which transmits and receives a radio wave between a
wireless access terminal in an area to convert this into a high
frequency signal, the RF unit 302 which modulates and demodulates
the high frequency signal to convert into a baseband signal having
a low frequency; the data Ch modulation unit 303 which modulates
transmit data to convert into a baseband signal; the control Ch
modulation unit 304 which modulates control information to convert
into a baseband signal; the control Ch demodulation unit 305 which
demodulates a received signal to extract control information; the
data Ch receiving unit 306 which demodulates and decodes a received
signal to extract received data; the data buffer 307 which
temporarily buffers transmit data; the channel processing unit 308
for transmitting data to a wireless base station controller; the
PER measuring unit 310 which calculates a packet error rate from a
data demodulation result in the data Ch demodulation unit; and a
power control unit 801 which determines a transmission power
correction value of a wireless access terminal based on the
information from the PER measuring unit and a sum of power-control
information retained thereinside. Upon receipt of a sum of
power-control information correction values from a wireless access
terminal after handoff, the base station inputs this into the power
control unit 801 to overwrite the sum of power-control information
retained thereinside.
It should be further understood by those skilled in the art that
although the foregoing description has been on embodiments of the
invention, the invention is not limited thereto and various changes
and modifications may be made without departing from the spirit of
the invention and the scope of the appended claims.
* * * * *